Lipid metabolism in the rumen.

Increasing the concentrations of beneficial polyunsaturated fatty acids in milk produced by dairy cows in high-forage systems

Publisher Summary This chapter discusses the biosynthesis of conjugated linoleic acid (CLA) in ruminants and humans. Conjugated linoleic acid is a mixture of positional and geometric isomers of linoleic acid with a conjugated double-bond system. Because of its potential to improve human health, there is great interest to increase the amount of CLA in the human food supply. This has caused great effort to be expended toward increasing the concentration of CLA, and more specifically rumenic acid (RA), in the milk and tissues of ruminant foods because these are the predominant source of CLA in human diets. RA is the predominant CLA isomer present in ruminant products, and the major source of its occurrence is endogenous synthesis via desaturation of vaccenic acid (VA) by ∆-9-desaturase. The chapter focuses on improving the understanding of biohydrogenation in the rumen and examining milk and tissue CLA responses to a range of diets. The diversity of various BH intermediates in digesta, milk, and tissues indicates the complexity of the BH processes as a whole and the population dynamics of the ruminal bacteria involved. Predicting the outcome of changes in the diet is complicated by the interactions of the ruminal environment, substrate supply and forms of dietary lipids, all of which influence the BH process simultaneously.

Biosynthesis of conjugated linoleic acid in ruminants and humans.

https://flore.unifi.it/retrieve/handle/2158/652014/20596/Buccioni%20et%20al%20%20Anifee%20Review%202012.pdf

Lipid metabolism in the rumen: New insights on lipolysis and biohydrogenation with an emphasis on the role of endogenous plant factors

As gut capacity is assumed to scale linearly to body mass (BM), and dry matter intake (DMI) to metabolic body weight (BM(0.75)), it has been proposed that ingesta mean retention time (MRT) should scale to BM(0.25) in herbivorous mammals. We test these assumptions with the most comprehensive literature data collations (n=74 species for gut capacity, n=93 species for DMI and MRT) to date. For MRT, only data from studies was used during which DMI was also recorded. Gut capacity scaled to BM(1.06). In spite of large differences in feeding regimes, absolute DMI (kg/d) scaled to BM(0.76) across all species tested. Regardless of this allometry inherent in the dataset, there was only a very low allometric scaling of MRT with BM(0.14) across all species. If species were divided according to the morphophysiological design of their digestive tract, there was non-significant scaling of MRT with BM(0.04) in colon fermenters, BM(0.08) in non-ruminant foregut fermenters, BM(0.06) in browsing and BM(0.04) in grazing ruminants. In contrast, MRT significantly scaled to BM(0.24) (CI 0.16-0.33) in the caecum fermenters. The results suggest that below a certain body size, long MRTs cannot be achieved even though coprophagy is performed; this supports the assumption of a potential body size limitation for herbivory on the lower end of the body size range. However, above a 500 g-threshold, there is no indication of a substantial general increase of MRT with BM. We therefore consider ingesta retention in mammalian herbivores an example of a biological, time-dependent variable that can, on an interspecific level, be dissociated from a supposed obligatory allometric scaling by the morphophysiological design of the digestive tract. We propose that very large body size does not automatically imply a digestive advantage, because long MRTs do not seem to be a characteristic of very large species only. A comparison of the relative DMI (g/kg(0.75)) with MRT indicates that, on an interspecific level, higher intakes are correlated to shorter MRTs in caecum, colon and non-ruminant foregut fermenters; in contrast, no significant correlation between relative DMI and MRT is evident in ruminants.

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A case of non-scaling in mammalian physiology? Body size, digestive capacity, food intake, and ingesta passage in mammalian herbivores ☆

Particulate fractions prepared from meadow hay, ranging in size from 0·1 to 2 mm, were incubated with rumen digesta from four cannulated Romney sheep fed the same hay. The rates of gas production, lipolysis of corn oil and hydrogenation of linoleic acid were measured.The rate of gas production per g fermentable particles (FP) was approximately 30% lower with 1–2 mm than with the 0·1–0·4 mm particles. However, per m2 surface area the rate for the larger particles was found to be approximately 600% greater.The rates of lipolysis of triacylglycerols and hydrogenation of linoleic acid were respectively 25 and 60% higher per g FP and 1100 and 1200% higher per m2 FP surface area with the 1–2 mm particulate fraction.The same hay particulate fractions were incubated with pure cultures of Ruminococcus flavefaciens, since this organism is active in both lipid metabolism and cellulose fermentation. The rate of gas production and the number of organisms adhering to the particles were determined.The effects of particle size on gas production were similar to those found when incubations were carried out with rumen digesta. Per g FP the rate was 40% lower with 1–2 mm than with 0·1–0·4 mm particles. However, per m2 surface area the rate was found to be approximately 450% greater with the former.It was further found that although the density of the bacterial population on 1–2 mm particles was 600% higher than on the 0·1–0·4 mm particles, the rate of gas production per 109 bacteria remained unchanged.We conclude that per m2 surface area fermentation, lipolysis and hydrogenation were more rapid with particles ranging from 1 to 2 than from 0·1 to 0·4 mm in size. This was due, at least in part, to microbial population density.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002185960007965X

Influence of particle size and surface area on in vitro rates of gas production, lipolysis of triacylglycerol and hydrogenation of linoleic acid by sheep rumen digesta or Ruminococcus flavefaciens

A. S. D. King

Papers

Influence of particle size and surface area on in vitro rates of gas production, lipolysis of triacylglycerol and hydrogenation of linoleic acid by sheep rumen digesta or Ruminococcus flavefaciens